These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Crash Bandicoot (1996)
Most Annoying Sound: Crash's "Ta-dadadaaaa!", which accompanies receiving crystals from perfect level runs.
Nintendo Hard: Crash 2 and 3 aren't by any means easy, but this game takes the cake. The fact that you can only save in bonus rounds makes it even worse. Gaining gems is also very different:
Brutal side paths that hold little value besides some crates you need to break to get the gem for the level. Later games would have no crates on these paths(most of the time) and give the player a second gem instead.
You have to finish the whole level from start to finish in one life, including levels like Sunset Vista which may be longer and is certainly more difficult than any single level in the second and third games.
In the second game it will tell you how many you're missing just before the finish, and the third game keeps count for you during the level. In here, there's no sign of whether you have all of the crates at the end of the level, just a message afterwards saying "Great! But you missed 4 [of the most cheaply hidden] crates [of all time]".
Then again, one has to remember that by not getting any boxes or gems, the player hasn't made any new progress and has nothing to really save. Tawna's tokens are so easily found in every level that it's almost impossible to miss them.
"Sunset Vista". Clearing it is fairly challenging. Getting the gem, much more so. Remember: To get the Gem, one must destroy every crate and not die after reaching a Checkpoint Crate. Also, this is one of only two levels with a Cortex bonus level, which are hard and mandatory for 100%.
"Slippery Climb" had another level called "Stormy Ascent" in its style that was Dummied Outbecause it was too difficult.
"Toxic Waste". You must avoid barrels that are thrown down the path by the other members of Pinstripe's mafia, and there are very few areas where you can hide from the barrels. It gets worse later on in the level, in which bouncing barrels are being thrown as well, and it takes lots of practice to memorize their patterns and where you can hide from them without being flattened.
"Fumbling in the Dark", the harder version of "Lights Out". Both levels are Exactly What It Says on the Tin in that the levels are pitch-black unless you have a mask, which lights up the general vicinity for a limited period of time. This means that you basically need to accomplish jumps quickly, with moving platforms and giant swinging blades, and if you get hurt, you lose your light source. That's bad enough, but Fumbling in the Dark in particular adds insult to injury by having some seriously hard jumps in the beginning of the level (behind the level's entrance), Checkpoint Starvation, and requiring a ton of timing and good reflexes. If you can beat Fumbling in the Dark and get the gem for it, chances are the rest of the game won't be very hard for you.